An element using a field emission cathode has larger electron mobility and more resistant to high speed and high temperature operation and radiation damage than a semiconductor element. Accordingly, it is being utilized in these days as a display element demanded to have high luminance and low electric power consumption.
FIG. 10 shows a perspective view of a structure of a part of a field emission cathode having been conventionally used.
The field emission cathode is constituted from an emitter tip 101 having an apex, an emitter electrode 102 for applying a negative voltage to the emitter tip, and a gate electrode 103 for withdrawing electron. Upon applying a voltage between the emitter tip 101 and the gate electrode 102 as shown in FIG. 10, a large electric field is applied to the apex of the emitter tip to cause electron release.
FIG. 11 shows a schematic structural view of a display device using the conventional field emission cathode.
A cathode plate 109 has a glass substrate 105 on which emitter electrodes 102 in a stripe form are formed and gate electrodes 103 are formed in a direction perpendicular to the emitter electrodes 102 with a dielectric layer 104 interposed between the emitter electrode 102 and the gate electrode 103. Micro cathode arrays (FEAs) each comprising plural field emission cathodes are formed at pixels 106, which are intersection points of the emitter electrodes 102 and the gate electrode 103.
Fluorescent materials 108 of three colors, red (R), green (G) and blue (B), are applied on a surface of an upper anode plate 107, and cause light emission when electrons emitted from the field emission cathodes strike the fluorescent layers 108.
In general, the field emission cathode is often produced by a production process developed by C. A. Spint, et al. FIG. 12 shows an explanatory diagram of steps of the production process of a field emission cathode (cathode plate) developed by C. A. Spint, et al.
In FIG. 12(a), an emitter power feeding film 117 is formed on a dielectric substrate 116 formed of glass or the like, and then patterned to form an emitter electrode 102 as in FIG. 12(b).
Thereafter, a dielectric film 118 and a gate power feeding film 119 are formed in this order by plasma CVD or the like as in FIG. 12(c).
The gate power feeding film 119 and the dielectric film 118 are separately etched by using a resist pattern having circular gate openings to form gate openings 120 in a cylindrical form having a diameter of about 1 μm as in FIG. 12(d).
Subsequently, a sacrifice layer material, such as aluminum, is obliquely deposited on the dielectric substrate 116 to prevent its deposition on the emitter power feeding film 117 in the gate openings 120 to form a sacrifice layer film 121 as in FIG. 12(e).
Furthermore, an emitter metal material 122, such as molybdenum, is perpendicularly deposited on the dielectric substrate 116 as in FIG. 12(f). At this time, the gate openings 120 are gradually plugged with the accumulated emitter metal material with the lapse of time, and when they are completely plugged, emitter tips 101 having a conical form are formed in the gate openings 120 as in FIG. 12(f).
The sacrifice layer 121 is then selectively dissolved with a phosphoric acid aqueous solution or the like to remove the emitter metal material 122 except the emitter tips 101 as in FIG. 12(g).
Finally, the gate power feeding film 119 is patterned to a desired shape to complete minute field emission cathodes as in FIG. 12(h) of the figure.
In this production process, however, so-called vacuum heating deposition is used for forming the emitter tips in the process step shown in FIG. 12(f), and in order to produce the emitter tips with high accuracy, it is necessary that the emitter metal material is deposited in a direction substantially perpendicular to the substrate by using an expensive deposition apparatus.
In other words, the production cost is difficult to reduce because of the formation step of the emitter tips.
Accordingly, an object of the invention is to realize simplification and cost reduction of the production process of a field emission cathode by forming protrusions capable of emitting electrons by using a material containing predetermined metal fine particles.